Tube For Heat Exchanger

ABSTRACT

A tube ( 10 ) for a heat exchanger is produced by folding a strip ( 11 ). One end ( 13 ) of the strip ( 11 ) is shaped in such a way as to constitute, after folding, a separating partition ( 12 ) having a curvilinear profile. According to one embodiment, the curvilinear profile is a looped profile, comprising a first part ( 12   a ) of loop and a second part ( 12   b ) of loop ending inside the first part ( 12   a ) of loop.

The present invention relates to a tube for a heat exchanger.

The invention has a particularly advantageous application in the fieldof flat tube heat exchangers. These exchangers are notably used asevaporators, condensers or forced air heaters in an air conditioningsystem of a motor vehicle, or as a radiator in the cooling circuit ofsuch a vehicle.

Flat tube heat exchangers for motor vehicles are generally constitutedby an array of flat tubes disposed parallel with each other in one ormore rows, these tubes being intended for the circulation through theexchanger of a heat transfer fluid, such as water with added glycol inthe case of radiators of engine cooling circuits. In cooling the devicesof the engine, the water heats up and must in its turn be cooled. It isthe role of the radiator to provide this function. For this purpose, thewater with added glycol is circulated in the tubes of the radiator andis cooled by heat exchange with cool air coming from a propellingdevice, or fan, the heat exchange being favored by the presence of heatexchange elements disposed in the array of tubes. In the case of aforced air heater, the thermal energy dissipated in the air is retrievedin order to heat the passenger compartment of a motor vehicle via aventilation, heating and/or air conditioning system which is known perse.

According to the heat exchanger assembly technology known as “bybrazing”, the tubes are brazed onto heat exchange elements constitutedby spacers or fins placed between the tubes. In general, these spacersare produced in the form of an undulating surface, the tubes beingbrazed onto the spacers at the peaks of the undulations. The assembly ofthe tubes and the spacers thus assembled by brazing is capped at eachend by a collector box connected by pipes to the rest of the circuit.

The flat tubes can be obtained by various techniques, like extrusion,mechanized welding or folding. The invention applies to this lattertechnique in which each flat tube is produced by folding a metal sheetcalled a strip in order to define a circulation duct for the heattransfer fluid, water in this instance. The strip is constituted from abase material otherwise called the core, generally an aluminum alloy.

The international application No WO 03/046456 proposes in particular aflat tube with a separating partition, produced from a strip of whichone end has been shaped such that the separating partition obtainedafter folding the strip has a curvilinear profile, substantiallysemicircular in shape.

However, despite all the advantages which it procures, the flat tubeknown from the international application No WO 03/046456 neverthelesshas the disadvantage of offering only a low mechanical resistance to theinflation of the tube resulting from the pressure applied by the heattransfer fluid. In fact, its curvilinear arc-of-circle shape providesthe separating partition with a certain flexibility favoring its openingup and therefore the inflation of the tube under the action of hydraulicpressure.

The opening up of the separating partition has the consequence ofcreating an asymmetry between the two circulation channels situated oneither side of the partition, whereas the hydraulic cross-sections ofthe channels must be equal and remain so no matter what the operatingphase of the heat exchanger may be.

Moreover, the inflation of the tube under pressure generates mechanicalstresses at several places, notably along the radii of the tube and onthe longitudinal weld at the junction between the two folded parts ofthe tube.

Finally, the repeated inflation/rest cycles accelerate the fatigue ofthe materials constituting the tube.

All of these phenomena consecutive to the inflation of the flat tubeweaken the mechanical strength of the heat exchanger and lead to theappearance of leaks.

Therefore, one objective of the invention is to propose a tube for aheat exchanger which would make it possible to avoid the disadvantagesrelated to the inflation under pressure of the tube described in theabovementioned international application, whilst retaining theadvantages of this tube, such as being free of dimensional toleranceconstraints in the width of the strip and/or the cladding with a brazingmaterial on just one of the two faces of the core.

This objective is achieved, according to the invention, by means of atube for a heat exchanger produced by folding a strip, one end of saidstrip being shaped in such a way as to constitute, after folding, aseparating partition having a curvilinear profile, noteworthy in thatsaid curvilinear profile is a looped profile, said separating partitionbeing closed on itself. This feature is explained by the fact that theedge of the strip used in the separating partition is sandwiched in aU-shaped fold, which makes it possible to put the cladding in contactwith the inside surface of the tube having no cladding and thus to widenthe brazing in order to achieve a high level of resistance to inflation.

Thus, as will be seen in detail below, it is possible, with the loopedcurvilinear profile conferred by the invention on the separatingpartition, to carry out a first brazing of the partition on the insidesurface of the tube in combination with a second brazing of the free endof the partition on itself. Because the invention prohibits by this factany possibility of opening the partition, the mechanical resistance ofthe latter to inflation of the tube is thereby considerably increased.

It will be noted that this result is obtained whilst retaining theadvantage of not having to clad both faces of the strip with brazingmaterial. One clad face suffices for the implementation of theinvention, the other face being able to receive a material limiting thecorrosion on the inside surface of the tube.

According to one embodiment of the invention, said looped curvilinearprofile comprises a first part of loop and a second part of loop endinginside the first part of loop.

In this particular embodiment, the invention makes provision for saidfirst and second parts of loop to have substantially an arc-of-circleshape in which the thickness of the strip is constant.

If an internal thickness of the tube is fixed in such a way as to imposea given hydraulic cross-section on the circulation channels, thedimensional characteristics of the separating partition must be adjustedaccordingly.

The invention therefore provides for said separating partition to havealong said loop a thickness less than the thickness of the tube, oragain for said separating partition to have a first thickness less thanthe thickness of the tube over the first part of loop, and a secondthickness less than the first thickness over the second part of loop.

The following description given with reference to the appended drawings,given as non-limiting examples, will give a good understanding of whatthe invention consists of and of how it can be embodied and willparticipate, if necessary, in the definition of the latter.

FIG. 1 is a partial cross-sectional view of a tube for a heat exchangeraccording to the invention.

FIG. 2 a is a partial cross-sectional view of a strip according to afirst embodiment of the invention.

FIG. 2 b is a partial cross-sectional view of a strip according to asecond embodiment of the invention.

In FIG. 1 there is shown partially in cross-section a flat tube 10 for aheat exchanger which can indifferently be an evaporator, a condenser, aforced air heater or a radiator of a motor vehicle.

The tube 10 is obtained by shaping and folding a strip 11 produced froma base material, or core material, which is generally an aluminum alloychosen from the series referenced 1xxx, 3xxx, 6xxx and 7xxx and whosemelting temperature is between 630 and 660° C.

Before shaping and folding, the strip 11 receives, on a first face 111which after folding constitutes the outside surface of the tube 10, alayer 21 of added material or cladding material, often call a “clad”,constituted by an aluminum alloy of the series 4xxx whose meltingtemperature is higher than 577° C. and lower than the meltingtemperature of the core metal. This layer 21 represents the actualbrazing layer which, by melting the added material in a furnace, willprovide the mechanical holding together of the heat exchanger whosecomponents, flat tubes and spacers in particular, are previouslyassembled. This brazing layer 21 is shown in bold line in the figures.

On a second face 112 of the strip 11, that is to say the inside surfaceof the tube 10 after folding which delimits the internal volume of thetube, there is deposited a layer 22 of a material making it possible toreduce the speed of propagation of corrosion through the core metal ofthe strip 11. This material, notably based on aluminum and silicon, hasa melting temperature higher than that of the brazing material or“clad”. This protective layer 22 is shown in dotted line in the figures.

As can be seen in FIG. 1, one end or edge 13 of the strip 11 is shapedin such a way as to produce, after folding, a partition 12 separatingthe tube 10 into two channels 31, 32 for the circulation of heattransfer fluid.

The separating partition 12 is closed upon itself in a loopedcurvilinear profile comprising a first part 12 a of loop substantiallyhaving an arc-of-circle shape and a second part 12 b of loop alsosubstantially having an arc-of-circle shape ending inside the first part12 a of loop. The arcs of circle have a curvature of about 180°.

It is therefore possible to braze the partition 12 in two zones, namelya first zone centered about the point A where the partition is brazed onthe inside surface 112 of the tube 10, and a second zone centered aboutthe point B where the partition is brazed at the end of the second part12 b of loop onto the inside surface of the first part 12 a of loop.

Starting from the outside surface of the tube, the separating partitioncomprises a first fold 41 at 45° towards the inside of the tube(clockwise direction) followed by a first flat section 42 and then asecond fold 43 at 45° turned towards the outside of the tube(anticlockwise direction), after which there is a second flat section 44which receives the edge of the strip not used in the separatingpartition. This second flat section 44 is an element of the first partof loop 12 a turned through 180° towards the inside of the tube,followed by a third flat section 45 whose outside surface makes contactwith the inside surface of the tube. This third flat section 45 iscommon to the first and to the second parts of loop 12 a and 12 b. Theprofile of the separating partition continues by the curvature of thesecond part of loop 12 b turned through 180° towards the inside of thetube (clockwise direction) and ends at the edge of the strip 46sandwiched between the second flat section 44 and the third flat section45.

In this way there is obtained a very rigid separating partition 12capable of resisting the pressure applied by the heat transfer fluid andtherefore of opposing any inflation of the tube 10, notably by theopening of the profile of the partition, such as occurs for the knowntube of the prior art. The hydraulic cross-section of the channels 31,32 is maintained and no transmission of stress to other elements of thetube occurs.

If the hydraulic cross-section of the channels 31, 32 is fixed, thelatter can be obtained by adjusting the thicknesses of the partition 12over the first 12 a and second 12 b parts of loop.

According to a first embodiment, the partition 12 can have a constantthickness e₂ along the loop (or the edge of the strip), this thicknessbeing less than the thickness e₁ of the tube 10. In this case, as shownin FIG. 2 a, the strip 11 has at the end or edge 13 a step change inthickness or shoulder between the values e₁ and e₂.

According to a second embodiment, which is shown in FIG. 2 b, thepartition 12 has a first thickness e₂ less than the thickness e₁ of thetube 10 over the first part 12 a of loop and a second thickness e₃ lessthan the first thickness e₂ over the second part 12 b of loop. In thiscase, FIG. 2 b shows two steps in thickness on the strip 11, one of thembetween the values e₁ and e₂, and the other one between the values e₂and e₃.

The thickness values are:

0.1 mm≦e₁ ≦0.4 mm

0.05 mm≦e₂ ≦0.4 mm

0.05 mm≦e₃ ≦0.4 mm

If the hydraulic cross-section of the channels 31 and 32 is not fixed,then e₁=e₂=e₃.If the hydraulic cross-section of the channels 31 and 32 is fixed orimposed, then the thicknesses are adjusted as follows:

e ₃ =e ₂ <e ₁   first embodiment

e ₃ <e ₂ <e ₁.   second embodiment

1. A tube (10) for a heat exchanger produced by folding a strip (11),one end (13) of said strip (11) being shaped in such a way as toconstitute, after folding, a separating partition (12) having acurvilinear profile, wherein said curvilinear profile is a loopedprofile, and said separating partition (12) is closed on itself.
 2. Thetube (10) as claimed in claim 1, wherein said looped curvilinear profilecomprises a first part (12 a) of loop and a second part (12 b) of loopending inside said first part (12 a) of loop.
 3. The tube (10) asclaimed in claim 2, wherein said first (12 a) and second (12 b) parts ofloop are substantially arc-of-circle shaped.
 4. The tube (10) as claimedin claim 3, wherein said second part (12 b) of loop is brazed against aninside surface of said tube (10).
 5. The tube (10) as claimed in claim4, wherein said second part (12 b) of loop is brazed on a second flatsection (44) which delimits the start of said first part (12 a) of loop.6. The tube (10) as claimed in claim 2, wherein said first part (12 a)of loop is constituted by a second flat section (44) followed by a curvethrough 180° which is followed by a third flat section (45) in commonwith said second part (12 b) of loop, wherein said third flat section(45) is followed by a curve through 180° which ends in a fourth flatsection (46) sandwiched between said second flat section (44) and saidthird flat section (45).
 7. The tube (10) as claimed in claim 1, whereinsaid separating partition (12) has along said loop a constant thickness(e₂) less than the thickness (e₁) of said tube (10).
 8. The tube (10) asclaimed in claim 2, wherein said separating partition (12) has a firstthickness (e₂) less than the thickness (e₁) of said tube (10) over thefirst part (12 a) of loop, and a second thickness (e₃) less than thefirst thickness (e₂) over the second part (12 b) of loop.
 9. The tube(10) as claimed in claim 1, wherein a first face (111) of the tube (10)is covered with a brazing layer (21) whilst a second face (112) of saidtube (10) is covered with a layer (22) protecting against corrosion,said second face (112) delimiting the internal volume of said tube (10).10. A heat exchanger able to exchange heat energy between a first mediumand a fluid which circulates inside a tube (10) as claimed in claim 1.11. The tube (10) as claimed in claim 3, wherein said first part (12 a)of loop is constituted by a second flat section (44) followed by a curvethrough 180° which is followed by a third flat section (45) in commonwith said second part (12 b) of loop, wherein said third flat section(45) is followed by a curve through 180° which ends in a fourth flatsection (46) sandwiched between said second flat section (44) and saidthird flat section (45).
 12. The tube (10) as claimed in claim 4,wherein said first part (12 a) of loop is constituted by a second flatsection (44) followed by a curve through 180° which is followed by athird flat section (45) in common with said second part (12 b) of loop,wherein said third flat section (45) is followed by a curve through 180°which ends in a fourth flat section (46) sandwiched between said secondflat section (44) and said third flat section (45).
 13. The tube (10) asclaimed in claim 2, wherein said separating partition (12) has alongsaid loop a constant thickness (e₂) less than the thickness (e₁) of saidtube (10).
 14. The tube (10) as claimed in claim 3, wherein saidseparating partition (12) has along said loop a constant thickness (e₂)less than the thickness (e₁) of said tube (10).
 15. The tube (10) asclaimed in claim 3, wherein said separating partition (12) has a firstthickness (e₂) less than the thickness (e₁) of said tube (10) over thefirst part (12 a) of loop, and a second thickness (e₃) less than thefirst thickness (e₂) over the second part (12 b) of loop.
 16. The tube(10) as claimed in claim 4, wherein said separating partition (12) has afirst thickness (e₂) less than the thickness (e₁) of said tube (10) overthe first part (12 a) of loop, and a second thickness (e₃) less than thefirst thickness (e₂) over the second part (12 b) of loop.
 17. The tube(10) as claimed in claim 2, wherein a first face (111) of the tube (10)is covered with a brazing layer (21) whilst a second face (112) of saidtube (10) is covered with a layer (22) protecting against corrosion,said second face (112) delimiting the internal volume of said tube (10).18. The tube (10) as claimed in claim 3, wherein a first face (111) ofthe tube (10) is covered with a brazing layer (21) whilst a second face(112) of said tube (10) is covered with a layer (22) protecting againstcorrosion, said second face (112) delimiting the internal volume of saidtube (10).